Creutzfeldt-Jakob Disease

Definition

Description

Before 1995, Creutzfeldt-Jakob disease was not well known outside the medical profession. Even within it, many practitioners did not know much about it. Most doctors had never seen a case. With the recognition of a so-called "new variant" form of CJD and the strong possibility that those with it became infected simply by eating contaminated beef, CJD has become one of the most talked-about diseases in the world. Additionally, the radical theory that the infectious agent is a normal protein that has been changed in its form also has sparked much interest.

First described in the early twentieth century independently by Creutzfeldt and Jakob, CJD is a neurodegenerative disease causing a rapidly progressing dementia ending in death, usually within eight months of symptom onset. It also is a very rare disease, affecting only about one in every million people throughout the world. In the United States, CJD is thought to affect about 250 people each year. CJD affects adults primarily between ages 50 and 75.

Spongiform encephalopathies

The most obvious pathologic feature of CJD is the formation of numerous fluid-filled spaces in the brain (vacuoles) resulting in a sponge-like appearance. CJD is one of several human "spongiform encephalopathies," diseases that produce this characteristic change in brain tissue. Others are kuru; Gerstmann-Straussler-Scheinker disease, a genetic disorder predominantly characterized by cerebellar ataxia (a kind of movement disorder); and fatal familial insomnia, with symptoms of progressive sleeplessness, weakness, and dysfunction of the nervous system that affects voluntary and involuntary movements and functions.

Kuru was prevalent among the Fore people in Papua, New Guinea, and spread from infected individuals after their deaths through the practice of ritual cannibalism, in which the relatives of the dead person honored him by consuming his organs, including the brain. Discovery of the infectious nature of kuru won the Nobel Prize for Carleton Gadjusek in 1976. The incubation period for kuru was between four to 30 years or more. While kuru has virtually disappeared since these cannibalistic practices stopped, several new cases continue to arise each year.

Cases of CJD have been grouped into three types: familial, iatrogenic, and sporadic.

Familial CJD, representing 5-15% of cases, is inherited in an autosomal dominant manner, meaning that either parent may pass along the disease to a child, who then may develop CJD later in life.

Iatrogenic CJD occurs when a person is infected during a medical procedure, such as organ donation, blood transfusion, or brain surgery. The rise in organ donation has increased this route of transmission; grafts of infected corneas and dura mater (the tissue covering the brain) have been shown to transmit CJD. Another source is hormones concentrated from the pituitary glands of cadavers, some of whom carried CJD, for use in people with growth hormone deficiencies. Iatrogenic infection from exposure to nerve-containing tissue represents a small fraction of all cases. The incubation period after exposure to the infectious agent is very long and is estimated to be from less than 10 to more than 30 years. It remains unlikely, but not impossible, that blood from patients with CJD is infectious to others by transfusion.

Sporadic CJD represents at least 85% of all cases. Sporadic cases have no identifiable source of infection. Death usually follows first symptoms within eight months.

Animal forms and "mad cow disease"

Six forms of spongiform encephalopathies are known to occur in other mammals: scrapie in sheep, recognized for more than 200 years; chronic wasting disease in elk and mule deer in Wyoming and Colorado; transmissible mink encephalopathy; exotic ungulate encephalopathy in some types of zoo animals; feline spongiform encephalopathy in domestic cats; and bovine spongiform encephalopathy (BSE) in cows.

BSE was first recognized in Britain in 1986. Besides the spongiform changes in the brain, BSE causes dementia-like behavioral changes—hence the name "mad cow disease." BSE was thought to be an altered form of scrapie, transmitted to cows when they were fed sheep offal (slaughterhouse waste) as part of their feed, but researchers believe it is a primary cattle disease spread by contaminated feed.

The use of slaughterhouse offal in animal feed has been common in many countries and has been practiced for at least 50 years. The trigger for the BSE epidemic in Great Britain seems to have come in the early 1980s, when the use of organic solvents for preparation of offal was altered there. It is possible that these solvents had been destroying the agent called a prion, thereby preventing infection, and that the change in preparation procedure opened the way for the agent to "jump species" and cause BSE in cows that consumed scrapie-infected meal. The slaughter of infected (but not yet visibly sick) cows at the end of their useful farm lives, and the use of their carcasses for feed, spread the infection rapidly and widely. For at least a year after BSE was first recognized in British herds, infected bovine remains continued to be incorporated into feed, spreading the disease still further. Although milk from infected cows never has been shown to pass the infectious agent, passage from infected mother to calf may have occurred through unknown means. Researchers also have tried to confirm how to stop infection of the human food chain once the disease spread among cows. In 2003, a study reported that it spread through nervous system tissue in processed meat and that proper temperature and pressure controls could help ensure safety of commercial beef.

Beginning in 1988, the British government took steps to stop the spread of BSE, banning the use of bovine offal in feed and other products and ordering the slaughter of infected cows. By then, the slow-acting agent had become epidemic in British herds. In 1992, it was diagnosed in more than 25,000 animals (1% of the British herd). By mid-1997, the cumulative number of BSE cases in the United Kingdom had risen to more than 170,000. The feeding ban stemmed the tide of the epidemic; however, the number of new cases each week fell from a peak of 1,000 in 1993 to less than 300 two years later.

The export of British feed and beef to member countries was banned by the European Union, but cases of BSE had developed in Europe by then as well; however, by mid-1997, only about 1,000 cases had been identified. In 1989, the United States banned import of British beef and began monitoring United States herds in 1990. In December 2003, the first and only case (as of late March 2004) of BSE was discovered in the United States. This prompted recommendations of new safeguards to prevent further spread. Among these were regulations banning animal blood in cattle feed.

Variant CJD: The human equivalent of mad cow disease

From the beginning of the BSE epidemic, scientists and others in Britain feared that BSE might jump species again to infect humans who had consumed infected beef. This, however, had never occurred in scrapie from sheep, a disease known for hundreds of years. In 1996, the first report of this possibility occurred and the fear seemed to be realized with the first cases of a new variant of Creutzfeldt-Jacob disease, termed nvCJD, now just vCJD. Its victims are much younger than the 60-65 year old average for CJD, and the time from symptom onset to death has averaged 12 months or more instead of eight. The disease appears to cause more psychiatric symptoms early on. EEG abnormalities characteristic of CJD are not typically seen in vCJD.

By early 2004, CJD had claimed 143 victims in Great Britain and 10 in other countries. It is of major concern that the number of cases per year seems to be increasing by a factor of 1.35 each year. The only known case in the United States to date had been acquired while the person had been in Great Britain.

Evidence is growing stronger that vCJD is in fact caused by BSE:

almost all of the cases so far have occurred in Great Britain, the location of the BSE epidemic

BSE injected into monkeys produces a disease very similar to vCJD

BSE and vCJD produce the same brain lesions after the same incubation period when injected into laboratory mice

brain proteins isolated from vCJD victims, but not from the other forms of CJD, share similar molecular characteristics with brain proteins of animals that died from BSE

Researchers now treat the BSE-vCJD connection as solidly established.

Assuming that BSE is the source, the question that has loomed from the beginning has been how many people will eventually be affected. Epidemiological models once placed estimates at tens of thousands, but in 2003, scientists predicted a quicker end to the epidemic and have substantially lowered the numbers expected to contract the disease. The exact incubation period of vCJD in humans is about 10 to 20 years or longer, so it is more difficult to predict the number of cases. Researchers know that some people are more susceptible to vCJD, including young people age 10 to 20 years old.

Causes and symptoms

Causes

It is clear that Creutzfeldt-Jakob disease is caused by an infectious agent, but it is not yet clear what type of agent that is. Originally assumed to be a virus, evidence is accumulating that, instead, CJD is caused by a protein called a prion (PREE-on, for "proteinaceous infectious particle") transmitted from victim to victim. The other spongiform encephalopathies also are hypothesized to be due to prion infection.

If this hypothesis is proven true, it would represent one of the most radical new ideas in biology since the discovery of deoxyribonucleic acid (DNA). All infectious diseases, in fact all life, use nucleic acids—DNA or ribonucleic acid (RNA)—to code the instructions needed for reproduction. Inactivation of the nucleic acids destroys the capacity to reproduce. However, when these same measures are applied to infected tissue from spongiform encephalopathy victims, infectivity is not destroyed. Furthermore, purification of infected tissue to concentrate the infectious fraction yields protein, not nucleic acid. While it remains possible that some highly stable nucleic acid remains hidden within the purified protein, this is seemingly less and less likely as further experiments are done. The "prion hypothesis," as it is called, is now widely accepted, at least provisionally, by most researchers in the field. The most vocal proponent of the hypothesis, Stanley Prusiner, was awarded the Nobel Prize in 1997 for his work in the prion diseases.

A prion is an altered form of a normal brain protein. The normal protein has a helical shape along part of its length. In the prion form, a sheet structure replaces the helix. According to the hypothesis, when the normal form interacts with the prion form, some of its helical part is converted to a sheet, thus creating a new prion capable of transforming other normal forms. In this way, the disease process resembles crystallization more than typical viral infection, in which the virus commands the host's cellular machinery to reproduce more of the virus. Build-up of the sheet form causes accumulation of abnormal protein clumps and degeneration of brain cells, which is thought to cause the disease.

The brain protein affected by the prion, called PrP, is part of the membrane of brain cells, but its exact function is unknown. Exposure to the infectious agent is, of course, still required for disease development. Prion diseases are not contagious in the usual sense, and transmission from an infected person to another person requires direct inoculation of infectious material.

Familial CJD, on the other hand, does not require exposure, but develops through the inheritance of other, more disruptive mutations in the gene for the normal PrP protein. The other two inherited human prion diseases, Gerstmann-Straussler-Scheinker disease and fatal familial insomnia, involve different mutations in the same gene.

The large majority of CJD cases are sporadic, meaning they have no known route of infection or genetic link. Causes of sporadic CJD are likely to be diverse and may include spontaneous genetic mutation, spontaneous protein changes, or unrecognized exposure to infectious agents. It is highly likely that future research will identify more risk factors associated with sporadic CJD.

Symptoms

About one in four people with CJD begin their illness with weakness, changes in sleep patterns, weight loss, or loss of appetite or sexual drive. A person with CJD may first complain of visual disturbances, including double vision, blurry vision, or partial loss of vision. Some visual symptoms are secondary to cortical blindness related to death of nerve cells in the occipital lobe of the brain responsible for vision. This form of visual loss is unusual in that patients may be unaware that they are unable to see. These symptoms may appear weeks to months before the onset of dementia.

The most characteristic symptom of CJD is rapidly progressing dementia, or loss of mental function. Dementia is marked by:

memory losses

impaired abstraction and planning

language and comprehension disturbances

poor judgment

disorientation

decreased attention and increased restlessness

personality changes and psychosis

hallucinations

Muscle spasms and jerking movements, called myoclonus, are also a prominent symptom of CJD. Balance and coordination disturbance (ataxia), is common in CJD, and is more pronounced in nvCJD. Stiffness, difficulty moving, and other features representing Parkinson's disease are seen and can progress to akinetic mutism, which is a state of being unable to speak or move.

Diagnosis

CJD is diagnosed by a clinical neurological exam and electroencephalography (EEG), which shows characteristic spikes called triphasic sharp waves. Magnetic resonance imaging (MRI) or computed tomography scans (CT) should be done to exclude other forms of dementia, and in CJD typically shows atrophy or loss of brain tissue. Lumbar puncture, or spinal tap, may be done to rule out other causes of dementia (as cell count, chemical analysis, and other routine tests are normal in CJD) and to identify elevated levels of marker proteins known as 14-3-3. Another marker, neuron-specific enolase, may also be increased in CJD. CJD is conclusively diagnosed after death by brain autopsy. Scientists are investigating whether testing lymphatic tissue such as the tonsil may be an early tool in vCJD diagnosis. Additionally, recent studies have suggested that other blood tests may be useful as well.

Treatment

There is no cure for CJD, and no treatment that slows the progression of the disease. Drug therapy and nursing care are aimed at minimizing psychiatric symptoms and increasing patient comfort. However, the rapid progression of CJD frustrates most attempts at treatment, since decreasing cognitive function and more prominent behavioral symptoms develop so quickly. Despite the generally grim prognosis, a few CJD patients progress more slowly and live longer than the average; for these patients, treatment will be more satisfactory. Scientists are investigating whether some medicines that can "break" the abnormal protein form may be useful and whether a vaccine could help.

Prognosis

Creutzfeldt-Jakob disease has proven invariably fatal, with death following symptom onset by an average of eight months. About 5% of patients live longer than two years. Death from vCJD has averaged approximately 12 months after onset. However, in 2003, clinicians reported improvement in a patient with vCJD who received a new experimental drug called Pentosan.

Prevention

There is no known way to prevent sporadic CJD, by far the most common type. Not everyone who inherits the gene mutation for familial CJD will develop the disease, but at present, there is no known way to predict who will and who will not succumb. The incidence of iatrogenic CJD has fallen with recognition of its sources, the development of better screening techniques for infected tissue, and the use of sterilization techniques for surgical instruments that inactivate prion proteins. Fortunately, scientists are making progress. In 2003, researchers announced that they had uncovered the basis for diagnosing, treating and possibly preventing prion diseases such as vCJD. Their research possibly could lead to a vaccine and immunotherapy drugs.

KEY TERMS

Autosomal dominant inheritance— A pattern of inheritance in which a trait will be expressed if the gene is inherited from either parent.

Encephalopathy— Brain disorder characterized by memory impairment and other symptoms.

Iatrogenic— Caused by a medical procedure.

Nucleic acids— The cellular molecules DNA and RNA that act as coded instructions for the production of proteins and are copied for transmission of inherited traits.

Strategies for prevention of vCJD are a controversial matter, as they involve a significant sector of the agricultural industry and a central feature of the diet in many countries. The infectious potential of contaminated meat is unknown, because the ability to detect prions within meat is limited. Surveillance of North American herds strongly suggests there is no BSE here, and strict regulations on imports of European livestock make future outbreaks highly unlikely. Therefore, avoidance of all meat originating in North America, simply on grounds of BSE risk, is a personal choice unsupported by current data.

Resources

PERIODICALS

Brown, Paul, et al. "Ultra-high Pressure Inactivation of Prion Infectivity in Processed Meat: A Practical Method to Prevent Human Infection." Proceedings of the National Academy of Sciences of the United States May 13, 2003: 6093-6095.

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Creutzfeldt-Jakob Disease

Creutzfeldt-Jakob disease

Definition

Creutzfeldt-Jakob disease (CJD) is a rapidly progressive disease causing damage to the brain. It is one of a group of rare diseases that affects humans and animals, known as transmissible spongiform encephalopathies (TSE) and is believed to be caused by a prion, a newly identified type of disease-causing agent. Creutzfeldt-Jakob disease is characterized by dementia and walking difficulties. Death can occur up to two years after the first symptoms; however, most people die within seven months. There is no treatment or cure.

Description

Creutzfeldt-Jakob disease is a serious progressive degenerative disorder of the brain that was first described in the 1920s by two German researchers, and is characterized by sudden development of rapidly progressive neurological and neuromuscular symptoms. When symptoms begin, affected individuals may develop confusion, depression , behavioral changes, impaired vision, and/or impaired coordination. As the disease progresses, there may be rapidly progressive deterioration of thought processes and memory (dementia), resulting in confusion and disorientation, impairment of memory control, personality disintegration, agitation, and restlessness. Affected individuals also develop neuromuscular abnormalities such as muscle weakness and loss of muscle mass (wasting); irregular, rapid, shock-like muscle spasms (myoclonus ); and/or relatively slow, involuntary, continual writhing movements, particularly in the arms and legs. Later stages of the disease may include further loss of physical and intellectual functions, a state of unconsciousness (coma), and increased susceptibility to repeated infections of the respiratory tract. In many affected individuals, life-threatening complications may develop less than a year after the disorder becomes apparent.

There are three main forms of CJD, each one with its distinctive basic features. The sporadic CJD, which accounts for approximately 85% of all cases worldwide and occurs by chance, is associated with the presence of a misshapen protein in the brain, known as a prion ("proteinaceous infectious particle"). Sporadic CJD cannot be caught from another person or animal, is not related to diet, nor can it be inherited. On the contrary, inherited (or familial) CJD accounts for 5–10% of all cases of CJD and is caused by a faulty gene called prion-related protein (PRPN) that is passed down from parents to their children in a dominant inheritance, which means patients will develop the disease if they inherit a defective gene from just one parent. Symptoms are similar to sporadic CJD, but they appear earlier and have a longer time course.

Unlike the previous two CJD forms, acquired CJD affects those people who have not inherited the condition by two other ways. The iatrogenic CJD occurs due to accidental infection after medical procedures such as human pituitary hormone injection or dura mater transplantation. The variant CJD (vCJD), a type of CJD that was first identified in 1996, is passed from cows with bovine spongiform encephalopathy (BSE, or "mad cow disease") to humans. The variant form affects mostly younger adults and has different clinical and pathological characteristics.

All forms of CJD can be present in a person for long periods (often more than 20 years) during which there are no symptoms. The duration of the illness before death varies from a matter of weeks (typical of sporadic CJD) to three to twelve months (typical of variant CJD). However, there have been exceptions in both types.

Demographics

CJD appears to affect males and females in equal numbers. It occurs worldwide with an incidence rate that has remained stable at approximately one case per million people, annually. It usually first appears in mid-life, beginning between ages 20 and 68, with the average age at onset of symptoms being around age 50. The onset of the iatrogenic form depends on the age of exposure.

Causes and symptoms

All forms of CJD are caused by the presence of a faulty protein in the brain, called prion. Prions occur in both a normal form, which is a harmless protein found in the body's cells, and in an infectious form, which causes disease. The harmless and infectious forms of the prion protein are nearly identical, but the infectious form takes a different folded shape. Sporadic CJD may develop because some of a person's normal prions spontaneously change into the infectious form of the protein and then alter the prions in other cells in a chain reaction by a mechanism that is not yet understood. Misfolded protein molecules then spread through the brain and stick together to form fibers and/or clumps called plaques that can be seen with powerful microscopes. These bundles of twisted protein disrupt brain cells and eventually leave large holes in the brain tissue, giving the brain a spongy appearance. Fibers and plaques may start to accumulate years before symptoms of CJD begin to appear. It is still unclear what role these abnormalities play in the disease or how they might affect symptoms.

About 5–10% of all CJD cases are inherited. These cases arise from a mutation, or change, in the gene PRPN that controls formation of the normal prion protein. While prions themselves do not contain genetic information and do not require genes to reproduce themselves, infectious prions can arise if a mutation occurs in the gene for the body's normal prions. If the prion gene is altered in a person's sperm or egg cells, the mutation can be transmitted to the person's offspring. Several different mutations in the prion gene have been identified. The particular mutation found in each family affects how frequently the disease appears and what symptoms are most noticeable. However, not all people with mutations in the prion gene develop CJD. This suggests that the mutations merely increase susceptibility to CJD and that other, still-unknown factors also play a role in the disease.

CJD does not cause any symptoms at first. The first symptoms to appear include slow thinking, difficulty concentrating, impaired judgment, memory loss, personality and behavioral changes, and difficulties with coordination and vision. These symptoms rapidly give way to increasing mental deficits leading to severe, progressive dementia (mental decline) associated with self-neglect, apathy or irritability, and prominent muscle spasms (myoclonus). Seizures commonly occur as the disease progresses. Symptoms continue to worsen until both mental and physical functions are lost; patients are completely bedridden, and eventually lapse into coma. Comatose patients may die as a result of infection associated with being immobile, such as pneumonia.

Diagnosis

There is currently no single diagnostic test for CJD. Indeed, the only definitive diagnosis can be assessed by a postmortem examination (autopsy) of the brain or examining a sample of brain tissue (brain biopsy ). However, CJD should be considered in adults who experience a sudden onset of rapidly progressive dementia and neuromuscular symptoms such as myoclonus.

An electroencephalogram (EEG) and a magnetic resonance imaging (MRI) scan may be useful in determining abnormalities in the brain. People may be diagnosed as having "probable CJD." Although not definitive, all those who have been diagnosed as probable CJD in life, and who subsequently had an autopsy, were found to have been a CJD patient. Genetic testing can be carried out in people suspected of having the inherited form of CJD, in order to increase certainty of diagnosis. Such people usually report a family history of the disease.

Iatrogenic CJD is usually diagnosed on the basis of the affected person's medical history. Those at risk include people having received hormones derived from humans before 1992, or dura mater transplant grafts before 1985.

Treatment team

A neurologist or a psychiatrist is normally the primary consultant for CJD, and continual nursing care may be necessary as disease progresses. Physical therapist may also be required.

Treatment

As of 2004, no treatment has been shown to be effective against CJD. Treatments are available to alleviate some symptoms, such as morphine for muscle pain , and clonazepam (Rivotril) or sodium valproate (Epilim) for jerky movements. A wide range of drugs has been tested for their ability to slow the progress of the disease, but none has been shown to be useful.

At present, care consists of managing the specific problems faced by patients with CJD. Speech therapy and occupational therapy may help, and the support of district nurses and social services is often invaluable for people with CJD and their caregivers.

Recovery and rehabilitation

Because CJD is an incurable, fatal disease with a fast progression, recovery and rehabilitation are not possible. The emphasis in treatment is placed upon comfort and support of the affected individual and the caregivers.

Clinical trials

As of mid 2004, there are no ongoing clinical trials for CJD.

Prognosis

The outcome for a person with CJD is usually very poor. Complete dementia commonly occurs within six months or less after the appearance of the first symptoms, with the person becoming totally incapable of self-care. The disorder is fatal in a short time, usually within seven months, but a few people survive as long as one or two years after diagnosis. The cause of death is usually infection, heart failure, or respiratory failure.

Special concerns

Hospitals and health care providers take special precautions to minimize the risk of transferring prions from surgical equipment or donated tissues. Medical histories of potential cornea donors that indicate a familial history of possible Creutzfeldt-Jacob disease rule out the use of those corneas for transplantation. Additionally, regulations and records regarding livestock feed and transfer of livestock are maintained by the United States Department of Agriculture.

Resources

BOOKS

Staff. The Official Patient's Sourcebook on Creutzfeldt-Jakob Disease: A Revised and Updated Directory for the Internet Age.San Diego: Icon Group International, 2003.

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Creutzfeldt-Jakob Disease

Encyclopedia of Aging
COPYRIGHT 2002 The Gale Group Inc.

CREUTZFELDT-JAKOB DISEASE

Creutzfeldt-Jakob disease is one of the transmissible spongiform encephalopathies, a family of diseases affecting humans and animals (see Table 1). They are transmissible, in that susceptible animals inoculated with diseased tissue will develop a similar disease; spongiform, in that, under a microscope, small spaces (vacuoles) in brain tissue are invisible, giving the appearance of a sponge; and encephalopathies, in that they affect the brain.

The disease was first reported by Hans Creutzfeldt in 1920 and Alfons Jakob in 1921. A related, exclusively familial disease, Gerstmann-Sträussler-Scheinker syndrome, was reported in 1928. Creutzfeldt-Jakob disease is a dementia characterized by a rapid progression and a multitude of varying cognitive and motor deficits.

The first advance in understanding the diseases occurred with the recognition that kuru, a disease afflicting only the Fore people of New Guinea, caused similar changes in brain tissue. Kuru is a rapidly progressive dementia (over months) characterized by cerebellar degeneration, causing clumsiness and difficulty walking (ataxia), tremor, and slurred speech. It has been linked to the Fore's practice of eating the brains of deceased relatives. Dr. D. C. Gadjusek, of the National Institutes of Health, hypothesized that ingestion of brain tissue caused the disease, and demonstrated in 1966 that inoculation of brain tissue from kuru patients into chimpanzees' brains caused the disease. Shortly afterward transmissibility was also demonstrated for Creutzfeldt-Jakob disease and Gerstmann-Str;äussler-Scheinker syndrome. Gadjusek and a colleague, Baruch S. Blumberg, were awarded the 1976 Nobel Prize in Medicine for this work.

Prions

The demonstration of transmissibility produced a search for the infectious agent. Initially researchers believed that a virus must be involved, but by the early 1980s the prion hypothesis had been proposed. "Prion" is a term coined by Dr. Stanley Prusiner in 1982 to indicate that the agent is both a protein and infectious. Prusiner, a University of California neurologist, received the 1997 Nobel Prize in medicine for his work on this new class of infectious agent.

The prion protein is a normal constituent of the human body, and although the exact function
is unknown, it is involved in neuron development and prevention of neuronal cell death. The abnormal form of the protein has an insoluble conformation; that is, the protein folds in such a way that it can not easily interact with other body molecules. Since the abnormal form is resistant to degradation by normal body enzymes, it is termed protease-resistant prion protein. The abnormal protein can both accumulate into plaques and induce normal prion protein, in a chain reaction, to transform into the abnormal conformation. The prion protein is concentrated in nervous tissue but can also be found in other tissues, particularly white blood cells and the lymphatic system.

The prion hypothesis explains many of the characteristics of the Transmissible Spongiform Encephalopathies: how a familial disease could be infectious (the inheritance is due to a mutation in the prion gene, but the resultant abnormal protein can induce the conformational chain reaction in people without the mutation); why the agent is so resistant to disinfection (most viruses or bacteria are more susceptible to heat or detergents than insoluble proteins are); and how a disease can be infectious without the involvement of any DNA. The best evidence for the prion hypothesis comes from work on self-propagating prions of yeast.

Clinical features

Creutzfeldt-Jakob disease occurs worldwide, with an incidence rate of one per million, most commonly between the ages of fifty and seventy. There are familial forms of the disease, due to mutations in the prion protein gene, best studied in populations in Slovakia and among Libyan Jews. The disease can be iatrogenic, caused by exposure to infectious tissue, such as corneal transplants, dura mater grafts, contaminated surgical instruments, and medications made from human brain tissue, most notably human growth hormone. The time between exposure and onset of the disease can be many years. Most cases, however, are sporadic, or random. There has never been a known case of person-to-person infection. Although it can theoretically be transmitted by blood transfusion, no such case has been identified. There was much interest in the 1970s and 1980s in dietary risk factors, particularly ingestion of animal brains, but this has not been supported by more recent studies. Preliminary data reported in September of 2000 suggest
that variant Creutzfeldt-Jakob disease can be passed on through blood transfusions and from a mother to her fetus.

The diagnostic criteria for Creutzfeldt-Jakob disease are presented in Table 2, and are self-explanatory. Often patients with Creutzfeldt-Jakob disease, particularly those with myoclonus, have a typical pattern of sharp waves on their electroencephalograph. Elevated levels of the 14-3-3 protein, a neuronal protein of unknown function, have been found in the cerebrospinal fluid of patients with Creutzfeldt-Jakob disease, and occasionally other cerebral diseases. If Creutzfeldt-Jakob disease is suspected, testing for this protein can help confirm the diagnosis.

Creutzfeldt-Jakob disease progresses rapidly, with a median duration from onset to death of four and a half months. There is no effective treatment for any of the Transmissible Spongiform Encephalopathies. Treatment is limited to comfort care and, if appropriate, genetic counseling. The search for possible therapies involves agents that may stimulate the body to break down the abnormal prion protein, that may disrupt the conformational chain reaction, or that may prevent spread of the prion to the nervous system in an exposed individual.

The epidemic of Bovine Spongiform Encephalopathy in the United Kingdom in the
1980s produced fears that this disease might enter the food chain, and affect humans and other species. This fear has proven true, although the eventual magnitude is as yet unknown. New diseases with prions identical to that causing bovine spongiform encephalopathy have been found in humans, cats, and zoo animals, most likely from prion-contaminated food. This new human disease, variant Creutzfeldt-Jakob disease, differs in that it typically affects people in their twenties and thirties; psychiatric symptoms are prominent; and the pathological appearance is different, with many prion protein-containing plaques found throughout the cortex. Only people with a prion protein gene coding for the amino acid methionine at codon 129 on both gene copies (homozygous for methionine) are susceptible to the disease. People homozygous for valine, or heterozygous for both valine and methionine, are not known to be susceptible to the new variant. Cases have occurred only in Great Britain and France. It is difficult to know if an epidemic will occur, but the incidence increased by 33 percent between 1994 and 2000. Some of this increase may reflect new diagnostic methods.

Not all scientists support the prion hypothesis. They hypothesize that a cofactor, probably a virus, is also present. The works by Manuelidis and Balter cited in the bibliography present these alternative views.

Manuelidis, L. "Dementias, Neurodegeneration, and Viral Mechanisms of Disease from the Perspective of Human Transmissible Encephalopathies." Annals of the New York Academy of Sciences 724 (1994): 259–281.

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Creutzfeldt–Jakob disease

Creutzfeldt–Jakob disease (CJD) A disease of humans characterized by dementia and destruction of brain tissue. It is now known to be caused by an abnormal prion protein and is transmissible, although there is also an inherited familial form. This rare disease typically affects middle-aged and elderly people and leads to rapid mental deterioration and death. The abnormal prion interferes with the structure of normal prion protein in brain tissue, resulting in accumulations of the protein and consequent tissue damage. In most cases the source of infection is unknown. However, it is well established that infection can result, for example, via injections of growth hormone derived from infected human cadavers. During the 1990s a novel form of the disease emerged, called ‘variant CJD’, which typically affects young healthy individuals. This is thought to be caused by consumption of beef products derived from cattle infected with bovine spongiform encephalopathy.

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Creutzfeldt-Jakob Disease

CREUTZFELDT-JAKOB DISEASE

DEFINITION

Creutzfeldt-Jakob disease (CJD; pronounced KROITS-felt-YAH-kop) is a highly infectious disease that affects the nervous system. It is related to a condition known as "mad cow disease."

Creutzfeldt-Jakob Disease: Words to Know

Encephalopathy:

A brain disorder characterized by loss of memory and other mental problems.

Iatrogenic:

Caused by a medical procedure.

Prion:

A form of protein that can cause an infectious disease.

DESCRIPTION

Before 1995 CJD was little known outside the medical profession. In fact, many doctors knew little about it and few of them had ever seen a case. In 1995 that situation changed, when a new form of the disease was discovered. That form is called "mad cow disease." It seemed that people could contract a new form of CJD by eating beef from cows that had "mad cow disease." Before long, CJD was one of the most talked about diseases in the world. In spite of that fact, relatively few people actually died from the new form of CJD.

Creutzfeldt-Jakob disease was first described in the 1920s. It affects the nervous system and progresses very rapidly. The major sign is dementia (pronounced dih-MEN-sha), or madness. Death usually occurs less than eight months after symptoms first appear.

The disease is very rare. No more than one person in a million is affected by it worldwide. In the United States, CJD is thought to affect about 250 people each year. It occurs in adults of all ages, but is rare in young adults.

Creutzfeldt-Jakob disease belongs to a group of diseases known as spongi-form encephalopathies (pronounced SPUN-jih-form in-se-fuh-LAH-puhtheez). This term refers to the appearance of the brain of a person who develops one of these diseases. Holes develop in the brain that then fill up with liquids, giving it a sponge-like appearance.

Cases of CJD have been grouped into three types: familial, iatrogenic (pronounced eye-a-truh-JE-nik), and sporadic.

Familial CJD accounts for 5 to 15 percent of all cases. It is an inherited disorder that often does not show up until a person is an adult.

Iatrogenic CJD occurs as the result of a medical procedure, such as a blood transfusion or organ donation. In these procedures, the patient receives blood or tissue from another person, the donor. In some cases, the donor may carry the agent that causes CJD. That agent can be passed on to the patient during the medical procedure. This source of CJD is relatively uncommon.

Sporadic CJD is the name given to any case of the disease where the cause is not known. It represents about 85 percent of all cases of CJD.

"Mad Cow Disease" in Animals

Spongiform encephalopathies also occur in animals. The disease that affects sheep is known as scrapie, and was discovered more than two hundred years ago. Other forms of spongiform encephalopathies infect elk, mule deer, domestic cats, mink, zoo animals, and cows. The form that affects cows is known as bovine (for cow) spongiform encephalopathy (BSE).

BSE was first recognized in Great Britain in 1986. Cows infected with the disease behaved in very peculiar ways: they dashed around and acted as if they had gone crazy, hence the name "mad cow disease."

Researchers soon discovered how "mad cow disease" is spread. At one time, the wastes produced in slaughterhouses were used to make animal feed.

That is, the feed given to domestic cows usually contained wastes obtained from the slaughter of other cows. Some of the slaughtered cows were infected with BSE, but they may not have shown any signs of the disease. Like kuru (see box: Kuru Among Cannibals), BSE has a very long incubation period.

By 1988 the British government realized that BSE was a serious problem. Cows had been eating contaminated feed for many years and animal feed companies continued to produce contaminated feed without realizing the dangers involved. The British government made the decision to slaughter all cows believed to be infected with BSE. There were two problems with this decision. First, most cows infected with BSE acted normally. The only way to know that they were infected was to kill them and analyze their brains. Second, BSE had already spread widely through British cattle. By one estimate, 25,000 cows in Great Britain had been infected with the disease by 1992. That number accounted for 1 percent of the total British herd. By 1997 that number had increased to 170,000 cows.

The Jump to Humans

The similarities between BSE and kuru are obvious. Both diseases are transmitted when a person or a cow eats the meat of another member of its species. Early on, medical researchers began to wonder if BSE could mutate (change) in some way so that it would infect humans as well as cows. That is, could it jump the species barrier between cows and humans.

In 1995 this question was answered. Reports began to appear of CJD-like symptoms in a few people in Great Britain. These people were all relatively young adults whose brain-wave tests were similar to those of patients with CJD. The people were diagnosed with a form of Creutzfeldt-Jakob disease called new-variant Creutzfeldt-Jakob, or nvCJD. Patients with this disease lived an average of twelve months, rather than eight. As of 1998, twenty-three patients had been diagnosed with nvCJD.

CAUSES

The search for the agent that causes the spongiform encephalopathies is one of the great medical stories of the twentieth century. At first, researchers suspected that the disease was caused by some kind of virus. But they had no success in locating a virus that could cause infections of this kind.

KURU AMONG CANNIBALS

A disease that belongs to the spongiform encephalopathies family is kuru. At one time, kuru was very common among the Fore tribe in Papua, New Guinea. The disease was spread in a very unusual way. Members of the Fore tribe were cannibals. As part of their culture, they ate the organs (including the brain) of their dead relatives. They believed this custom was a way of honoring the dead. Thus, the disease spread from infected individuals after their death.

Kuru fascinated medical researchers, who discovered that the incubation period for the disease is incredibly long. The incubation period is the time it takes for symptoms to appear after a person has been infected. In the case of kuru, the incubation period is between four to thirty years or more, which means an individual infected with the disease may not show any symptoms for a very long time. This discovery earned Carleton Gadjusek the Nobel Prize in 1976 and introduced researchers to

One theory proposed as early as 1981 was regarded as a "crackpot" idea by many scientists. This theory was developed by the American biologist Stanley Prusiner. Prusiner suggested that spongiform encephalopathies might be caused

by certain kinds of protein molecules. Proteins are chemicals that perform many essential functions in the body. Prusiner suggested the name prion for the infectious forms of proteins.

Many researchers did not take Prusiner's idea seriously because no form of protein had ever been found to cause any infectious disease. After more than fifteen years of research, however, Prusiner's theory was confirmed. Unusual types of protein were finally discovered in the brains of animals with various kinds of spongiform encephalopathies. Scientists now believe that kuru, BSE, nvCJD, and related diseases are caused by the transmission of prions from an infected person to a healthy person. In the vast majority of cases (sporadic CJD), no one knows how this transmission occurs.

SYMPTOMS

About 1 in 4 people with CJD shows relatively mild symptoms of the disease at first. These symptoms include a generalized weakness, changes in sleep pattern, weight loss, or loss of appetite or sexual drive. Vision problems are also common.

Eventually, the most common symptom of CJD appears. This is dementia, or loss of mental function. Dementia is marked by:

Memory loss

Decreased ability to do abstract thinking and planning

Problems with language and comprehension (understanding)

Poor judgment

Disorientation (confusion)

Decreased ability to pay attention and increased restlessness

Personality changes

Hallucinations

Physical symptoms may also appear. These symptoms include muscle spasms, jerking movements, problems with balance and coordination, and muscle stiffness.

DIAGNOSIS

Creutzfeldt-Jakob disease is usually diagnosed by means of an electroencephalogram (EEG; pronounced ih-LEK-tro-in-SEH-fuh-luh-gram). An EEG is a procedure in which wires are attached to the brain. These wires detect electrical activity taking place in the brain. Certain distinctive patterns in the EEG are an indication of CJD.

CJD can be confirmed in an autopsy. An autopsy is a medical examination carried out on a dead body to determine what caused death. The autopsy can reveal the presence of abnormal proteins in the person's brain.

TREATMENT

There is no cure for CJD. There is also no treatment that will slow the progress of the disease. Drug therapy can be used to help some of the psychiatric symptoms of the condition. The fundamental problem, however, is the speed with which the disease develops. In most cases, there is relatively little time to try any form of treatment that can provide patients with much relief from their symptoms.

PROGNOSIS

Creutzfeldt-Jakob disease is always fatal. The typical survival time is eight months after symptoms first appear. About 5 percent of patients live longer than two years. The usual survival time for patients with nvCJD is twelve months after onset (beginning).

PREVENTION

Since the causes of sporadic CJD are not known, there is no known way to prevent the disease. Cases of iatrogenic CJD can be prevented by screening donor tissue for possible infection. Standard sterile procedures can also provide some protection against possible transmission of the disease during surgery. Since CJD is a genetic disorder, there is no way to prevent the condition. However, couples who wish to have children may want to be tested for the presence of a defective CJD gene.

Methods for preventing the spread of nvCJD are under considerable debate. In Great Britain, the government ordered the slaughter of tens of thousands of cows in the hopes of wiping out the disease by killing all animals that carried the prions that caused it. But the cost to the livestock industry was enormous. And, in most cases, no one really knew which cows were infected and which were not.

Other nations have tried to protect themselves from infected British cows. They have passed laws preventing the shipment of beef from Great Britain. So far, these laws appear to have been relatively effective. BSE and nvCJD have not yet broken out in other parts of the world.

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Creutzfeldt-Jakob disease

Creutzfeldt-Jakob disease (CJD) (kroits-felt yak-ob) n. a disease in which rapid progressive degeneration of brain tissue results in dementia and eventually death. It is caused by an abnormal prion protein (see spongiform encephalopathy). Most cases occur sporadically but some forms of CJD are inherited and a few are acquired. variant CJD (vCJD) the human form of bovine spongiform encephalopathy (BSE): a form of CJD believed to be acquired by ingestion of infected beef products. [ H. G. Creutzfeldt (1885–1964) and A. M. Jakob (1884–1931), German psychiatrists]www.cjd.ed.ac.uk Website of the national CJD surveillance unit

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Creutzfeldt-Jakob disease

Creutzfeldt-Jakob disease (CJD) Rare, degenerative brain disease that causes physical deterioration and dementia, usually progressing to death within a year of onset. Caused by an abnormal protein called a prion, it is related to scrapie in sheep, and bovine spongiform encephalopathy(BSE) – ‘mad cow disease’. Typically it affects older people, but in 1996 scientists found a new variant form of CJD (nvCJD) in younger victims. In 1997 research confirmed that the agent responsible for this variant was identical to that of BSE, confirming the link between CJD and the consumption of infected beef. There is no known cure.

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Creutzfeldt-Jakob disease (CJD) is a very rare disorder that damages the tissues of the brain, causing a rapid decline in mental function and muscle coordination, eventually leading to death. It is believed that a tiny transmissible* protein particle called a prion triggers the disease, which is divided into three categories:

Familial CJD accounts for up to about 10 percent of cases. In these instances, there exists a family history of the disease, suggesting that certain genes* shared by family members make them more susceptible to CJD.

(JEENS) are chemical structures composed of deoxyribonucleic acid (DNA) that help determine a person’s body structure and physical characteristics. Inherited from a person’s parents, genes are contained in the chromosomes found in the body’s cells.

Sporadic cases, in which people have no known risk factors for the disease, make up about 85 percent of occurrences.

Acquired CJD is the rarest form. Less than 5 percent of all cases result from exposure to infected brain or spinal tissue, usually during a medical procedure.

CJD belongs to a family of illnesses known as transmissible spongiform (SPUN-jih-form) encephalopathies (en-seh-fuh-LAH-puh-theez). Spongiform refers to the appearance of brain tissue affected by the disease—the damaged tissue is full of holes, much like a sponge. Other diseases in the CJD family include kuru*; bovine spongiform encephalopathy (BSE), which infects cattle and is known as mad cow disease; and scrapie*, which affects sheep. The disease generally affects people age 60 or older, but in 1996 scientists described a new form of CJD, called variant CJD or new variant CJD (vCJD). Variant CJD differs from classic CJD in that it typically affects people under the age of 30 and causes different symptoms. So far, cases of vCJD have been limited mostly to the United Kingdom and France, and all the people in whom vCJD has developed have been exposed to areas where BSE has been found.

Although CJD may be transmissible, it does not appear to spread through usual types of direct person-to-person contact. CJD can be transmitted through contact with infected brain or central nervous system* tissue or fluid, usually during a medical procedure. For example, the disease has been reported after cornea* transplants and dura mater*grafts*, following injection of human pituitary*–derived growth hormone*, and after contact with medical instruments used during brain surgery on a person with the disease. Cerebrospinal fluid can spread CJD, but there is no evidence of transmission through other body fluids, including saliva, blood, or urine. Variant CJD has occurred only where cases of BSE also have been found, leading researchers to theorize that eating beef from cattle with BSE could spread the agent and lead to CJD in humans. Although this explanation is widely accepted, it has not been proved.

is a chemical substance produced by the pituitary gland that regulates growth and other body functions.

Mad Cow Disease and the Human Connection

A disease called bovine spongiform encephalopathy (BSE or mad cow disease), which is similar to CJD but is found in cattle, has been linked to variant CJD. Cattle had long been fed ground-up carcasses from sheep and other livestock as a nutritional supplement. This practice may have caused an epidemic of BSE among cows in the United Kingdom that began in 1986. It is thought that the carcasses fed to the cows could have been those of animals infected with various forms of transmissible spongiform disease. In 1988 this feeding practice was banned in the United Kingdom. Millions of cows have since been slaughtered to protect the food supply, and the number of new BSE cases has dropped sharply.

The most characteristic symptom of CJD is quickly worsening dementia*, including memory loss and impaired thinking. Patients often have problems with vision and muscle coordination. The inability to sleep, unusual sensations, and depression are also common. Many patients experience muscle jerking known as myoclonus (my-AH-kloh-nus), which consists of brief, rapid muscle contractions. If the disease is contracted from human tissue (such as from a transplanted cornea), symptoms may not appear for decades after exposure to the contaminated tissue. Variant

(dih-MEN-sha) is a loss of mental abilities including memory, understanding, and judgment.

Prions: Are They “Infectious”?

Like bacteria, viruses, and parasites, prions, which are abnormal protein particles, have been linked to certain transmissible diseases. Yet prions are different from other infectious agents. While microorganisms* contain genetic material, prions do not, which means that they are not alive. According to the prion theory, the protein at first cannot transmit disease. Instead, it undergoes a change that allows it to fold into a different shape, its “infectious” form. When a prion enters a brain cell in the course of CJD, it binds to normal proteins, causing them to change shape. This sets off a chain reaction leading to cell death and the release of more prions to enter and affect more cells. As cells die, holes form in brain tissue giving it the characteristic “spongelike” appearance. Prions can be acquired during a medical procedure or from some other exposure to brain tissue or fluids containing brain tissue. In the inherited form of CJD, it is believed that a gene mutation* allows some normal proteins to change into prions under certain conditions.

CJD at first causes psychiatric (sy-kee-AH-trik) symptoms, such as depression, anxiety (ang-ZY-uh-tee), or personality changes; dementia and myoclonus typically occur later than in classic CJD.

Variant Creutzfeld-Jakob disease has occurred only where cases of bovine spongiform encephalopathy also have been found, leading researchers to theorize that eating beef from cattle with BSE could spread the agent. In France and England whole herds of cattle have been put to death in an effort to prevent the spread of disease. AP/Wide World Photos

CJD can be diagnosed by a brain biopsy (BI-op-see), which requires removing a small piece of brain tissue during surgery to examine for signs of the disease, or by an autopsy*. Other, less invasive tests may point to a diagnosis of CJD or help identify another cause of the patient’s symptoms, such as meningitis or encephalitis. During a physical examination, the doctor checks for muscle twitching and spasms. An eye exam may show areas of blindness that the patient may not have noticed, and a spinal tap* and blood tests may identify certain proteins associated with CJD. An electroencephalogram (EEG) test records electrical activity in the brain and may show a pattern of brain waves seen in many patients with CJD, although the typical EEG findings are not present in vCJD. Some people with CJD have negative test results, making a diagnosis difficult without a brain biopsy.

also called a lumbar puncture, is a medical procedure in which a needle is used to withdraw a sample of the fluid surrounding the spinal cord and brain. The fluid is then tested, usually to detect signs of infection, such as meningitis, or other diseases.

Because CJD cannot be cured, the goal of treatment is to make the patient as comfortable as possible. Medications can help control aggressive behavior, lessen pain, and ease muscle jerks. Dementia can progress to loss of speech, the inability to take care of oneself, blindness, and even coma. As patients become bedridden, they are vulnerable to infections, such as pneumonia, and most eventually need to be hospitalized. Many patients die within a year after symptoms appear.

Genetically Engineered Bacteria to the Rescue

Growth hormone once was obtained from the pituitary glands of cadavers—that is, the bodies of people who have died—and patients who needed injections of growth hormone were at risk of getting CJD. Now growth hormone can be produced in laboratories by inserting the genes controlling the production of growth hormone into bacteria, thus avoiding the need to extract the hormone from human tissue and eliminating the risk of transmitting CJD.

No known measures can prevent the onset of CJD in a person whose brain tissue contains the prion. Because the ways by which the disease can be transmitted are still not well understood, blood banks forbid people with confirmed or suspected CJD or those who may be at high risk, such as persons with a family history of the disease, to donate blood, and doctors advise that they not be organ or tissue donors. Family members of a person with CJD may wish to have genetic counseling to learn more about any family risk. Special handling of surgical instruments can limit the chance of transmission during certain medical procedures, particularly those involving the brain.

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